Impulse transmitter



March 10,'1942. f VELEGG 2,275,448

IMPULSE TRANSMITTER Filed April 17, 1940 M ll/ENTOR ME. LEGG Byj. %(c

TTORNEV Patented Mar. 10, 1942 UlTEiD] STATES P'TENT V f OFFICE.

Telephone Laboratories,

Incorporated, New

York, Y., a corporation of NewYork Application April 17, 1940, Serial No. 330.045 2 claims. l(Cl. 179-90) This invention relates to mpulse transmitters and more particularly to electricalimpulse transmitters commonly known as telephone calling dia-ls.

An object of the invention is to provide an improved device of this character.

A feature of theinvention resides in an arrangement for operating the impulse contacts by a rotatng permanent magnet, these contacts being made of magnetic material and preferably enclosed in a hermetically sealed tube.

A further feature resides in an electrodynamic braking device for governing the rate of producing the impulses. i

In the Vusual callng dial arrangement the speed of operation is controlled by a mechanical governor and the impulse contacts are mechanically connected to be operated by a rotatng member of the dial. Also in the usual arrangement the switch contacts are exposed within the set housing and are thus exposed to dust.

In accordance with this invention, the impulse contacts are operated by a permanent magnet carried by a rotatng member ofthe dial. Preferably the contacts are enclosed in a hermetically sealed container which may contain a suitable gas at proper pressure or be evacuated. Preferably the switch pcomprises Overlapping spaced finger-like flexible contacts, all or part of which are of magnetic material. The contacts are held closed when the magnet is in position to cause an appreciable magnetic fiux to traverse the magnetic material of the contact members and opened when the magnet is moved to a position substantially reducing the magnetic fiux traversing the magnetic material of the contact members. The bar magnet, near the magnetic contact members, having its axis of rotation through its center or neutral point and this point directly over the junction of the reedlike contact members, produces when the magnet and the contact members are in a more or less relatively parallel position, a maximum magnetic force between the members and causes their spaced Overlapping ends to come together, while rotatng the magnet to a position substantially at right angles to the contact members balances out the magnetic attracting force between them and permits their contacts to open. The fiexible reed-like contact members are so mounted that their Overlapping contact ends are spaced apart when practically no magnetic flux is passing through them. Other relative movements than rotation between the permanent magnet and the switch contact members are possible, but

as the telephone dial employs rotatng members, a rotary, movement of the permanent magnet is particularly applicable and simple.

Oneform of sealed switch whichv meets the requirements above stated consists of a small glass'tube with'iron reeds respectively supported atjand extending from the opposite ends of the tube into Overlapping spaced relatonship and attractable Vtogether magnetically. Such a switch is disclosed in the pending patent application of Walter B. Ellwood, Serial No. 198,629, filed March 29, 1938. i

The electrodynamic speed governor employs the rotatable permanent magnet above mentioned-and an electrically conductive surrounding housing in which eddy currents generated by the rotation of the magnet retard its rotation.

Fig. 5 is a side and partial section view taken generally on lines 5-5 of Fig. 4.

Similar reference characters refer to the same parts in the diiferent drawing figures.

l The electrical impulsex transmitter disclosed herein is of the finger-Wheel type shown in patents to Forsberg 1,161,854, issued November 30, .1915, and to Dobbin and Gent 1,390,679, issued September 13, 1921. The arrangement shown in this application differs primarily from that shown in the patents referred to above by replacng the mechanically operated impulse contacts by magnetically operated impulse contacts and if desredthe mechanical friction type speed control governor by an electrodynamic governor. The other parts of the dial mechanism may be substantially as shown in these patents. The chief advantages of these improvements have already been pointed out.

v Referring to the drawing figures, the dial mechanism is mounted on the cup-shaped housing or base member lfl. The finger wheel l l is concentrically positoned above the housing Ill and rigidly attached to rotatable shaft l2. A

switch ac.

helical spring I3 concentrically positioned with respect to this central shaft I2 is arranged to restore it and the attached finger wheel II to their normal rest position whenever the dial is displaced therefrom for operating the impulse mechanism. A gear Wheel I 4, rigidly mounted on the shaft I2, engages pinion I rigidly mounted on shaft IS which is journaled in bearing supports I'I and I8. The ratio of the diameters of the gears I4 and I5 is such that movement of the finger-wheel I I from one digit to the next causes one-half a revolution of shaft I6. A barshaped permanent magnet 20 having a transverse hole through its center or neutral point is loosely mounted on shaft IS but is so connected therewith that it rotates with the shaft Vonly when the dial II is automatically returning to normal positon and the calling pulses are being produced. This one-way rotation of the bar magnet may be seecured by pawl and ratchet mechanism. A ratchet Wheel I9 attached to shaft IG and resiliently engaged by pawl 2I attached to the permanent magnet 20 causes the magnet to rotate in the one direction. A second ratchet .Wheel 23 attached to the bar magnet 20 and resiliently engaged by pawl 24 attached to the fixed bearing support I8, prevents rotation of the magnet when the dial I I is being manually operated or set to select a certain digit. The magnet 20 should come to rest in position to hold the contact members 3I and 32 of switch 30 closed. To assure this, a leaf spring 26 attached to the base I0 is so postioned with respect to the knob 21 on the gear M as to be engaged when the dial is in the non-operated position. This knob moves the spring into the circular path of the lugs 28 near the ends of the magnet 20 and causes the magnet to come to rest in a position substantially parallel to the reed contacts of the The bar magnet thus rotates only when the dial is returning to normal position and calling pulses are being produced and electrodynamic governing of the speed of rotation of the dial mechanism is taking place and comes to rest in the same angular position. The spaced and overlappingly mounted contact members 3I and 32 of the sealed switch 30 are in close proximity to the bar magnet 20. As earlier referred to heroin one form of this switch element may be that known as the Ellwood relay. The portion of the operating cycle during which the contacts are closed and are opened may be determined by the rpositon of the relay with reference to the rotating bar magnet. This is an important feature and provision is made for adjusting the relative fixed position of therelay and the magnet. The relay switch -30 is held by support 33 which is adjustably attached to the base 50 by screw 34 or other suitable means. A slot 35 in support 33 through which the clamping screw extends permits moving the relay to- Ward or away from the axis of rotation of the magnet 20 and thus provides for timing the operation of the switch contacts since the distance the relay is positioned from the axis of rotation .determines the relative duration of closure of the contacts in an operative cycle.

Figs. 2 and 3 show the relay 30 and the bar magnet 20 parallel to each vother and in such relationship that a maximum magnetic force is holding the contact reeds 3I and 32 closed. Fig. 4 shows the relay and the magnet at right angles to each other and in this neutral relationship a minimum magnetic force is exerted on the reeds and they stand apart and the circuit is opened. The bearing support I8 is omitted from Figs. 3 and 4.

A speed governor for controlling the rate at which the calling. pulses are produced is necessary and as heretofore stated the rotatable permanent magnet 20 which operatesthe relay switch may also be used as part of an electrodynamic device for controlling the speed of operation of the mechanism. The magnet is circumferentially closely surrounded by a fixed copper ring 25 attached to the base I0. As the magnet is rotated part of its exterior magnetic field cuts the surrouncling conductor 25, producing eddy currents therein, and results in damping the speed of rotation. 'The surrounding conductor 25 may have a bottom to add to the damping effect. Such aV governing arrangement tends to cause a uniform speed of rotation and eliminates mechanical friction parts vwhich wear out of adjustment.

Contact springs 4I and 42 supported by base I0, shown in Fig. 2, are provided for connection with the telephone set in such a manner as to short-circuit its transmitter while signaling pulses `are being sent. They are allowed to close when the dial i I is moved out of its normal position by roller on a 'crank arm attached to shaft I 2 which normally keeps these contact springs open. Contact springs 43 and 44, also operated by the action of roller 40, open the circuit through the telephone receiver when the dial II is moved out of its normal position.

Also, as shown in Fig. 2, a terminal strip to which leads from contacts l3I and 32 of the switch 32 and from contact springs 4I to 44, is provided on the outside of base I0 for making connections leading from the telephone instrument. I

What is -claimed is:

1. In an impulse transmitter device in which magnetically operable switch contacts are magnetically operated by means of a rotatable permanent magnet bar, a ring of non-magnetic electrical conducting material extending around said magnet bar and defining a space in which said magnet bar loperates, said ring and said magnet bar being arranged to produce in said ring eddy currentsV during the rotational movements of said magnet bar and said eddy currents operating directly on said magnet bar to reduce the rspeed of rotation of said magnet bar.

2. In a telephone calling dial device in which magnetically operable switch contacts are magnetically roperated by means of a centrally pvoted rotatable permanent magnet bar controlled in its Operation by means of a rotatable fingerwheel, a stationary ring of non-magnetic electrical conducting material encircling said magnet bar and defining an operating space for said magnet bar, saidvring vbeing so arranged relative to said magnet bar that eddy currents are produced in said ring when said magnet bar is rotated, the eddy currentsproduced in said ring directly operating on said magnet bar to reduce the speed of rotation of said magnet bar so that said switch contacts are operated at a required speed.

VICTOR E. LEGG. 

